Telephone system



.NOV. 5, 1935. w DARROW ET AL 2,19,561

TELEPHONE SYSTEM Filed Nov. 2, 1933 4 Sheets-Sheet l THRU OTHER DIAL JACKS IO/ n-- w. 5. DA RR on MEMO "G.H. PETERSON ATTORNEY 4 Nov. 5, 1935. w. E. DARROW ET AL 2,019,561

TELEPHONE SYSTEM Filed Nov. 2, 1933 4 Sheets-Sheet 2 W.'.DARROW it a. H. PETERSON Nov. 5, 1935. w. E. DARROW ET AL 2,019,561

TELEPHONE SYSTEM WE. DARROW il 6.11. PETERSON Nov. 5, 1935. -w. E. DARROW ET AL 2,019,561

TELEPHONE SYSTEM Filed Nov. 2, 1933 4 Sheets-Sheet 4 THPU OTHER DIAL JACKS 70 NIGHT ALARML'KZ' .WE. DARROW 6.11. PETERSON A TTORNEV Patented Nov. 5, 1935 UNITED STATES TELEPHONE SYSTEM Application November 2, 1933, Serial No. 696,414

11 Claims.

This invention relates to telephone systems and more particularly to those in which impedance devices, such as repeating coils, are used in the trunks or other connecting circuits over which conversational connections are established.

The object of the invention is to protect the subscribers or operators, who may be engaged in setting up a connection, from disagreeable noises in their telephones due to changes of current which it is necessary to effect in the circuits involving repeating coils or other impedance devices.

Systems have been devised heretofore in which relays are used for controlling the circuits in such a way as to avoid a sudden change in the flow of current through one side of a repeating coil, such as would be caused by the closing or opening of the circuit, while the other side of said coil is in telephonic connection with a subscribers or an operators telephone. In certain systems, however, as for example those in which trunk lines extend between a small magneto oifice and a dial office it is desirable to minimize the use of relays in the magneto ofiice as much as possible or in some cases to eliminate them entirely, thus avoiding the use of a separate source of power to operate them which otherwise would be unnecessary. At the same time it is necessary for the operator in the magneto exchange to connect and disconnect her dial to and from these trunks, thus opening and closing a circuit through the repeating coil.

According to the present invention these conditions are met by means of a circuit arrangement in which the plug and jack used for connecting the operators dial cord to the trunk effect a definite sequence of circuit changes whereby current may be changed in one side of the repeating coil without inducing disturbing currents in the other side of said coil. More specifically stated, the windings of the repeating coil are so connected to the spring contacts of the dial jack that, when the operator inserts the plug to connect the dial to the trunk, the tip of the plug engages the ring spring of the jack and opens the subscribers side of the coil slightly before it engages the tip spring to break the circuit over which current is flowing through the trunk side of said coil. Conversely, when she removes the plug at the completion of dialing, the tip of said plug disengages the tip spring of the jack to reestablish the circuit for the fiow of current through the trunk side of the coil slightly before it disengages the ring spring to reclose the subscribers side of said coil. This enables the current changes to be effected at a time when the subscribers and the operators telephones are disconnected telephonically from the repeating coil, thus safeguarding them 5 against the objectionable noises to which they would otherwise be subjected.

Other features of this invention will appear more fully from the following detailed description and also from the appended claims.

The invention has been illustrated in the accompanying drawings in which Fig. 1 shows a manual subscribers station A, a portion of a cord circuit C, dialing cord circuit Cl and the manual exchange equipment of a 15 two-way multiple trunk circuit terminating at its distant end in a mechanical exchange.

Fig. 2 shows the mechanical exchange equipment of the two-way trunk of Fig. 1 together with the switches necessary for completing an 20 incoming or outgoing call. Since the switches at the mechanical office form no part of the present invention they have been only diagrammatically represented.

Fig. 3 is a non-multiple adaptation of that 25 part of the trunk circuit shown in Fig. 1.

Fig. 4 is a modification of the system of Figs. 1 and 2 combined.

Referring now to the drawings, description will be made: First, of the operation of the cir- 30 cuits shown when a connection is established between the manual exchange station A and the mechanical exchange station B through the cord circuit C and two-way trunk of Figs. 1 and 2; second, of the operation taking place when a connection is established between the manual exchange station A and the mechanical exchange station B through the cord circuit C of Fig. l and two-way trunk of Figs. 3 and 2; and third, of the operation taking place when a connection is established between the manual exchange station A and the mechanical exchange station Bi through the cord circuit C of Fig. 1 and the twoway trunk of Fig. 4.

It is assumed then that subscriber A in the manual exchange desires to communicate with subscriber B in the mechanical exchange. The manual operator responds to the line signal (not shown) by inserting plug I83 of cord circuit C into jack I04, and with talking key I2l operated obtains the desired station number. The connection is extended to the trunk circuit by inserting plug Iol of cord circuit C into outgoing trunk jack IEO, whereupon relay Nil will be energized over an obvious path to connect battery to test pin I I2, over a path from battery through inner armature and front contact of said relay to the test pin, the function of which is to indicate a busy condition of the trunk at its multiple appearances. Subscribers station A, which is of the magneto type, will be telephonically connected to the trunk over a path from the sleeve of jack I00, lower left winding of repeating coil II3, top normally made contacts of jack I05, upper left winding of repeating coil II3, tip of jack I00, tip of plug IOI, tip of plug I03, tip of jack I04, subscribers station A, sleeve of jack I 00, sleeve of plug I03, sleeve of plug IOI to sleeve of jack I00. Relay I01 operated also disconnects the ringing relay I09 from the trunk side of repeating coil H3, and closes a circuit for operating incoming selector relay 2 I2 over a path from battery through right winding of said relay, lower armature and back contact of relay 200, trunk conductor I20, lower normally made contacts of dialing jack I05, lower right winding of repeating coil H3, middle armature and front contact of relay I01, resistance H8, upper closed contacts of jack I 00, upper right winding of repeating coil H3, trunk conductor II 9, upper armature and back contact of relay 200, thence to ground through left winding of relay 2I2.

In order to set the incoming selector and connector switches IS and IC, respectively, on the desired subscribers station terminals, a dialing means, comprising dial D, to which is attached dialing cord CI and plug I06, is used. Said dialing means is associated with the trunk circuit through the medium of dialing jack I05. When the plug I06 of dialing cord CI is inserted into dialing jack I05 the following sequence of three circuit operations takes place: First, the left windings of repeating coil I I3, which are included in the circuit for subscribers station A, are opened by the top opened contacts of dialing jack I05. Second, the contacts of dial D are connected to trunk conductors I I9 and I20 over a circuit traced from trunk conductor H9, sleeve of dialing jack I05, sleeve of dialing cord plug I08, contacts of dial D, tip of dialing cord plug I06, tip of dialing jack I05 to the trunk conductor I20. Third, the bridge circuit, comprising right windings of repeating coil I I3 and resistance II8, extending to trunk conductors H0 and I20, previously traced, is opened by the lower opened contacts of dialing jack I05. The switches IS and IC, at the mechanical exchange, respond to the dial to locate the desired station terminals, in the wellknown manner, after which the dialing cord circuit CI is removed from the dialing jack I05, restoring the circuit to the condition as described prior to dialing.

With current flowing in the trunk side of repeating coil II3, any change of current through said side of the coil, such as is effected when the dialing cord is associated with the trunk circuit, produces, by transformer action to the line side of said coil, objectionable acoustic disturbances, to both the operator and subscriber. In order to eliminate this undesirable condition the windings of the repeating coil I I3 are connected to the contacts of the dialing jack I05 so that a definite sequence of circuit operations is obtained when the dialing cord CI is associated with the trunk circuit. The dialing jack I05 is so constructed that when the tip of the dialing plug I00 engages the ring contact of dialing jack I05 the line side of repeating coil H3 is disconnected telephonically slightly before the tip of said plug engages the tip contact of said jack to break the circuit over which current is flowing through the trunk side of said coil. Conversely, when the dialing cord is removed from the dialing jack I05 the tip of dialing plug I06 disengages the tip spring of jack I05 to reestablish the circuit for the flow of current through the trunk side of repeating coil H3 slightly before the tip of said plug disengages the ring spring of said jack to reestablish telephonically the circuit for the operator and subscriber, through the line side of said coil. In this manner both the subscribers and operators telephones are disconnected from the repeating coil I I3 at a time when the current flow in the trunk side of said coil is of a transient nature and productive of said objectionable acoustic disturbances. When the dialing cord circuit CI is removed from the dialing jack I05 subscriber A will converse with subscriber B, upon the removal of the latters switchhook. After completion of the conversation the operator at the manual exchange will remove plugs WI and I03 of cord circuit C from jacks I00 and I04 respectively, thereby restoring all relays at the manual end of the trunk circuit to normal and opening the bridge across the trunk side of repeating coil I I3. The release of the switches IS and 10 at the mechanical exchange is effected in the well-known manner.

It will now be assumed that a subscriber B at the mechanical exchange, desiring a connection with subscriber A at the manual exchange, has dialed, and has obtained connection to the trunk by means of the selector switch OS in the wellknown manner. Relay 20! operates over a path traced from battery through winding of said relay, lower .armature and back contact of relay 2 I0, lower right winding of repeating coil 2H), middle brush of selector switch OS, subscribers loop (not shown) upper brush of selector switch OS, upper right winding of repeating coil 2I0, upper armature and back contact of relay 2M thence through winding of relay 2I3 to ground. Relay 20I closes an obvious circuit for operating relay 202 which extends its operating ground to the lower brush (sleeve) of the selector OS to maintain said selector busy. Relay 202 closes an obvious circuit for operating relay 200 and also closes a. circuit for operating relays 205 and 208- over a path extending from ground on upper outer armature and front contact of relay 202, upper inner armature and make-before-break contacts of relay 209, one path extending through winding of relay 203 to battery, and the other through lower make-before-break contacts of relay 205 through winding of relay 200 to battery. Relay 200 disconnects the incoming selector IS from the trunk conductors I I9 and I20 and connects said conductors to a source of ringing current 2| I over a path traced from right side of said ringing source, upper outer armature and back contact of relay 209, upper armature and front contact of relay 200, trunk conductor I I9, upper right winding of repeating coil IE0, and thence in parallel, one path extending through condenser IIS, and the other through condenser III, winding of ringing relay I09, middle armature and back contact of relay I01, to lower right winding of repeating coil II 3, lower normally made contacts of dialing jack I05, trunk conductor I20, lower armature and front contact of relay 200, lower inner armature and back contact of relay 209 to left side of ringing source 2I I. Ringing current is transmitted to the trunk over the path just described, for a sufficient length of time to operate ringing relay W9 at the manual exchange end of the trunk, thereby operating relay i l and locking said relay over .a path traced from battery through winding and right armature and front contact of said relay to ground through outer armature and back contact of relay I01. Relay 295 operated, operates relay 201 and the latter relay operates relay 2%. Relay 205 looks through its lower make-before-break contacts to ground on the upper outer armature and front contact of relay 202, over a path previously traced, and releases relay 2%. Relay 29S releases relay 201 and thereby closes .an energizing circuit for relay 209 over a path traced from ground through make-before-break contacts of relay 201, upper armature and front contact of relay 205 to battery through winding of relay 2B9. Relay 299 locks through its upper inner make-beiore-break contacts to ground on upper armature and front contact of relay 282. Relay 239 operated releases relays 2G5 and 298, removes the ringing source 25! from the trunk conductors HS and 20, and closes said conductors to the upper and lower left windings of repeating coil 2H9 respectively. Relays 295, 205 and 2!}? are slow acting in order to insure that ringing current will be applied to the trunk for a suflicient interval of time.

Returning to the manual exchange end of the trunk we find that relay Hi3 operated closes an energizing circuit for the drop ill over a path traced from ground on left outer armature and front contact of relay 1 lil, through winding of said drop to battery. Relay Elli also connects battery to busy test pin I I2, in order that the trunk will test busy for outgoing trafiic, over a circuit traced from battery left inner armature and front contact of relay i ill to test pin l l2. The manual exchange operator responds to the operated drop by inserting the plug Hit of cord circuit C into answering jack Hi2.

Relay l6! operates and, in addition to its previously described functions, it opens the locking circuit for relay Ill). Relay H6 released opens the operating circuit for the drop Ill and removes means for applying battery to the busy test pin IE, but since cord circuit C is now connected to the trunk this test potential is maintained on said test pin by relay in! as previously described. Relay ill! also closes a supervisory circuit, including resistance l M and signal M3 at the manual exchange and relays 253 and 2nd at the mechanical exchange, over a path traced from battery and lower winding of relay 254, lower winding of marginal relay Z63, lower left winding of repeating coil 2 I ii, lower inner armature and front contact of relay 289, lower armature and front contact of relay 2520, trunk conductor I20, lower normally made contacts of dialing jack I05, lower right winding of repeating coil l l3, middle armature and front contactof relay Hi1, winding of signal in upper closed contacts of answering jack E62, resistance lid, upper right winding of repeating coil H3, trunk conductor H9, upper armature and front contact of relay 205i, upper outer armature and front contact of relay 2B9, upper left winding of repeating coil 2m, upper winding of marginal relay 293, to ground through upper winding of relay 2M. Relay 2% operates over the path just described, but since relay 293 and signal Hi8 are both marginal said relay and signal will not operate in series with high resistance H4. The operation of relay 234 provides an independent means for energizing relay rec in order to maintain a busy condition on the lower brush (sleeve) of selector switch OS in the event that the calling subscriber B should disconnect first and thereby release relays 253i and 292. This circuit istraced from ground on make-beforebreak contacts of relay 2%, armature and front contact of relay 20 i thence through the upper inner make-before-break contacts and Winding of relay 209 to battery. The call is completed with cord circuit C to subscriber A in the usual manner and when the subscriber at A responds, the operator will be apprised of this condition by means of talking key it! of cord circuit C, with which she monitors on the connection. In order to set up a charge condition at the mechanical exchange end of the trunk the operator will depress non-locking charge key H5, which short circuits high resistance sufiicient current to flow through the signal I08 and marginal relay 203 to cause the operation of said signal and relay. The signal 08 operated provides an obvious path for maintaining the short circuit around resistance H 5 and at the same time provides means for indicating that a charge condition has been applied. Relay 203, at the mechanical exchange, operated, closes a circuit for operating relay 2M over a path traced from battery and winding of said relay, armature and front contact of relay 2B3 thence to ground through make-before-break contacts of relay 208. Relay 2M operated reverses battery and ground toward the originating subscriber to set up a charge condition for the call in the .well-known manner. Conversation between subscriber A and B takes place and when the mechanical subscriber hangs up and the manual operator disconnects the cord circuit C from the trunk all apparatus is restored to normal.

If a connection is desired from the manual exchange subscriber A to a mechanical exchange subscriber B over the two-way non-multiple trunk shown in Figs. 3 and 2, the operations of the trunk circuit of Fig. 3 are practically identical with those as described for the trunk circuit of Fig. 2, except that when the cord circuit plug Id! of cord circuit C is inserted into outgoing trunk jack 3% a circuit is closed to operate incoming selector relay 2 l2 over a circuit traced from battery through right winding of said relay, lower armature and back contact of relay 289, trunk conductor 3H, lower normally made contacts of dialing jack 3!, lower right winding of repeating coil 3%, upper closed contacts of outgoing trunk jack 398, winding of signal 393, upper right winding of repeating coil see, trunk conductor 3H], upper armature and back contact of relay 2%, to ground thru left winding of relay 2| 2. The dialing cord circuit Ci is then associated with the trunk circuit and the incoming selector and connector switches IS and IC, respectively, are set in the usual manner, after which the dialing cord circuit Cl is removed from the trunk circuit. All of the subsequent operations, for an outgoing call, are substantially the same as described for the trunk circuit of Fig. 1.

For a call from mechanical exchange station E to manual exchange station A the selector switch OS is set on the terminals of the trunk, and ringing current is transmitted to the trunk conductors 3H and 3H as previously described for the trunk circuit of Figs. 1 and 2. The circuit for rating ringdown drop is traced from trunk conductor 3H1, upper right winding of repeating I M, thereby allowing coil 3%, thence in parallelQone path extending contacts of outgoing trunk jack 300, to lower right winding of repeating coil 366, thence through lower normally made contacts of dialing jack 30! to trunk conductor 35 l. The manual operator, being apprised of an incoming call by the operation of the ringdown drop, responds by associating cord circuit C with the trunk circuit by inserting plug iii! of said cord circuit into answering jack 362, an action, which opens the circuit of ringdown drop 359 atlower opened contacts of said jack, and closes .a supervisory bridge, comprising signal 383, resistance 3% and right windings of repeating coil 3i across trunk conductors $58 and 3H by means of upper closed contacts of said jack. The circuit of this bridge is traced from trunk conductor 3! l, lower normally made contacts of dialing jack 38d, lower right winding of repeating coil 3G5, lower normally made contacts of outgoing trunk jack. 36B, upper closed contacts of answering jack 3112, resistance see, winding of signal 363 thence to trunk conductor 3!!) through upper right winding of repeating coil From trunk conductors are and 3 the bridge circuit is extended to the mechanical exchange end of the trunk as previously traced. Subsequent operations of the circuit such as the charging operation and disconnect features are the same as described for the trunk circuit of Fig. l.

The two-way trunk circuits, just described, are of the ringdown type, that is, ringing current is applied at the mechanical exchange portion of.

the trunk circuit to signal the manual exchange operator. A description will now be made for the interconnection of manual exchange subscriber A with mechanical exchange subscriber C by means of cord circuit C, dialing cord circuit Cl and the two-way multiple trunk of Fig. 4 which employs the well-known reversed battery and ground type of supervision. Since the method of interconnecting subscriber A with subscriber C is identical with that previously de scribed for the ringdown type of trunk circuit, only those features of difference such as supervision, etc., will be discussed in detail.

Assume that a connection is desired between manual exchange subscriber A and mechanical exchange subscriber Bl. Subscriber A is associated with the trunk circuit through the medium of cord circuit C, cord circuit plug l [H and trunk jack 4%. Relay dill is operated and battery potential is applied to test pin 353 through closed contacts of trunk jack iiii over obvious circuits. Relay dill, through its outer armature and front contact, short circuits the left high resistance winding of polarized relay 495 allowing sufiicient current to flow to operate incoming selector relay M2 over a path traced from battery and right winding of said relay, lower armature and back contact of relay 4! i, trunk conductor 4H3, lower normally made contacts of dialing jack 482, lower right winding of repeating coil 464, outer armature and front contact of relay dill, right winding of polarized relay 4%, upper right winding of repeating coil 4%, trunk conductor 389, upper armature and back contact of relay ll I thence to ground thru left winding of relay M2. Polarized relay 4% due to the direction of current flow will not operate at this time. The manual exchange operator associates the dialing cord Cl with the trunk circuit through the medium of dialing jack 582, performs the dialing operation, and removes the dialing cord Cl from the trunk circuit as previously described. When mechanical exchange subscriber Bl removes the re- -mechanical exchange subscriber Bl.

ceiver from the switchhook the connector switch 10! reverses battery and ground to trunk conductors 409 and H8 (apparatus not shown) to operate polarized relay 4% over a path which previously included incoming selector relay M2 5 but now includes the connector relay (not shown) with battery and ground reversed. The operation of polarized relay 386 operates relay 4B1. Relay is? looks over a circuit traced from battery through winding, and inner right armature and 10 front contact of said relay to ground through inner armature and. front contact of relay 4!. Relay 467 also closes a parallel path for maintaining a test potential on test pin 403 over a circuit traced from battery outer left armature l5 and front contact of relay 581, to test pin 403. This path is necessary to maintain a busy condition on the test pin until the mechanical exchange subscriber disconnects. Conversation. takes place and when mechanical exchange subscriber Bi disconnects, battery and ground from the connector switch 1C! are again reversed causing the release of polarized relay 486. This relay closes a circuit for operating signal 405 over a circuit traced from ground on armature and back contact of polarized relay 506, outer right armature and front contact of relay 401, lower closed contacts of trunk jack 400, through winding of signal 405 to battery. The signal 405 indicates a disconnect condition to the manual exchange operator who breaks down the connection in the usual manner restoring all apparatus to normal.

The operation of the circuit will now be described for a call originated by subscriber Bl at the mechanical exchange for the manual exchange subscriber A. Assume that mechanical exchange subscriber B! has dialed the proper code for extending a connection to the manual exchange, in which subscriber A is located, and 4.0 that selector switch OS! is set on the terminals associated with a trunk to said manual exchange. Relays 4H and 4M will operate (circuits not shown) from the selector OS l under control of The operation of relay ll 5 disconnects the trunk conductors M39 and MG from the incoming selector IS! and connects these conductors to the upper and lower right windings of repeating coil 5 respectively. The operation of relay M l reverses battery and ground to the trunk conductors 4139 and All! over a circuit from battery, lower winding of marginal relay 6E3, upper armature and front contact of relay M4, upper left winding of repeating coil H5, upper armature and front contact of relay 2M, trunk conductor 4-89, upper right winding of repeating coil 484, right and left windings of polarized relay 5%, lower right winding of repeating coil 4M, lower normally made contacts of dialing jack M2, trunk conductor H0, lower armature and front contact of relay 4, lower left winding of repeating coil 4 45, lower armature and front contact of relay M4 thence to ground through upper winding of marginal relay 3. Polarized relay 4B5 operates over the circuit just 05 traced, but, due to the high resistance of the left winding of said relay the marginal relay M3 does not operate. The operation of polarized relay 486 operates relay dill, and the latter relay closes a circuit for the signal 405 and night alarm relay 3578 over a path traced from ground, through winding of night alarm relay 408, left inner armature and front contact of relay 46?, middle armature and back contact of relay Ml to battery through winding of signal 405. The manual exchange operator is apprised of an incoming call by the signal 405 and associates the cord circuit C with the trunk circuit as described for an outgoing call. Relay 49! operates, and, in addition to the features described for an outgoing call, opens the circuit for night alarm relay 408 and signal 805. Marginal relay M3 receives suificient current at this time to operate, due to the short circuit connected to the left high resistance winding of polarized relay 486 by the outer armature and front contact of relay Mil, as previously described. Relay 413 causes the trunk circuit at the mechanical exchange to assume a condition for communication (apparatus not shown). Conversation and disconnection take place and the apparatus is restored to normal as heretofore described.

It will be understood that the invention is not limited to the specific embodiments herein shown and described. It should not be limited to use in any particular kind of telephone system nor to any specific type of operators position. The kind of switching or other connection establishing equipment is obviously immaterial to this invention, nor is it limited to means for eliminating noise-s produced by repeating coils. Moreover this invention is not limited to the use of plugs and jacks for securing the desired sequence of operations but may be embodied in other forms of connecting devices.

What is claimed is:

1. The combination in a telephone system of a telephone, an impedance device, an incoming circuit extending from said telephone to said impedance device, a second circuit outgoing from said impedance device, a controlling device, and a switch comprising a movable elementand a stationary element for connecting said controlling device to said outgoing circuit, said stationary element including contact members so arranged that when said movable element is brought into engagement with said stationary element it actuates first one of said contact members to open said incoming circuit to disable said telephone and then another of said contact members to open said outgoing circuit.

2. The combination in a telephone system of a telephone, an impedance device, an incoming circuit extending from said telephone to said impedance device, a second circuit outgoing from said impedance device, a controlling device, a stationary switch element having a contact member for closing said outgoing circuit and a second contact member for closing said incoming circuit, and a movable switch element for connecting said controlling device to said stationary element, said contact members being so arranged that when said movable element is disengaged from said stationary element it first controls the movement of said first mentioned contact member and then the movement of said second mentioned contact member to close the circuit from said telephone to said impedance device.

3. The combination in a telephone system of a telephone, an impedance device, an incoming circuit extending from said telephone to said impedance device, a second circuit outgoing from said impedance device, a jack having one contact member for opening said incoming circuit and another contact member for opening said outgoing circuit, a controlling device, and a plug for connecting said controlling device to said jack, said contact members being so arranged that first one and then the other of them is actuated by said plug.

'4. The combination in a telephone system of a telephone, an impedance device, an incoming circuit extending from said telephone to said impedance device, a second circuit outgoing from said impedance device, a jack having one contact for controlling said incoming circuit and a second contact for controlling said outgoing circuit, a controlling device, and a plug for connecting said controlling device to saidjack, said jack contacts being so arranged that the insertion of said plug first operates the first mentioned contact to open the incoming circuit and then the second mentioned contact to open the outgoing circuit.

5-. The combination in a telephone system of a telephone, an impedance device, an incoming circuit extending from said telephone to said impedance device, a second circuit outgoing from said impedance device, a jack having one contact for controlling said incoming circuit and a second contact for controlling said outgoing circuit, a controlling device, and a plug for connecting said controlling device to said jack, said jack contacts being so controlled by the insertion and withdrawal of said plug that the incoming circuit is always opened before and closed after the outgoing circuit.

6. The combination in a telephone system of a telephone, an impedance device, an incoming circuit extending from said telephone to said impedance device, a second circuit outgoing from said impedance device, a jack having tip and ring springs for controlling said circuits, a controlling device, and a plug for connecting said controlling device to said jack, said springs being so arranged that the plug first engages the ring spring to open the incoming circuit and then the tip spring to open the outgoing circuit.

'7. The combination in a telephone system of .a telephone, an impedance device, an incoming circuit extending from said telephone to said impedance' device, a second circuit outgoing from said impedance device, a jack having tip, ring and sleeve terminals connected to said incoming .and outgoing circuits, a controlling device, and a plug for connecting said controlling device to said jack, said tip and ring terminals being so arranged that the tip of the plug first engages the ring terminal to open the incoming circuit and then the tip terminal to open the outgoing circuit.

8. The combination in a telephone system of a repeating coil having two windings, an incoming circuit including one of said windings, an outgoing circuit including the other of said windings, a jack having one contact member for opening and closing said incoming circuit and another contact member for opening and closing said outgoing circuit, a circuit controlling mechanism, and a plug for connecting said mechanism to said jack, said contact members being so arranged that first one and then the other of them is actuated by said plug.

9. In combination, a telephone, a repeating coil having a plurality of windings, an incoming circuit including one of said windings, means for associating said telephone with said circuit, an outgoing circuit including another of said windings, a source of current in said outgoing circuit, a jack having one terminal for opening and clos-l ing said incoming circuit and another terminal for opening and closing said outgoing circuit, an impulse device for sending impulses over said outgoing circuit, and a plug for connecting said impulse device to said jack, said terminals being so arranged that first one and then. the other is engaged by said plug.

10. The combination with an operators position of a trunk terminating in a jack thereat, a repeating coil in said trunk, a cord circuit at said position having a plug for extending a connection by way of said jack through one of the windings of said coil, means responsive to the insertion of said plug in the jack for completing a circuit through another winding of said coil, a second jack for said trunk having one set of contact springs for controlling the circuit through said first mentioned winding and another set of springs for controlling the circuit through said second mentioned winding, a dial for sending impulses over said trunk, and a plug for connecting said dial to the last mentioned jack, said springs being so arranged that one set is opened before the other on insertion of the plug and closed after the other on removal of the plug.

11. The combination in a telephone system of an operators position, an automatic switch, a

trunk terminating at one end in a jack at said position and in said switch at the other end, a repeating coil in said trunk, means at the operators position for completing a circuit by way 01 said jack through a winding of said coil, means for completing a circuit through a second winding of said coil, a second jack for said trunk having one contact spring for opening and closing the circuit through said first mentioned winding and another contact spring for opening and closing the circuit through said second winding, a dial for sending impulses over said trunk to set said automatic switch, and a plug for connecting said dial to the trunk by way of said last mentioned jack, said springs arranged for engagement and disengagement by the plug in such an order that the circuit of said first winding is opened before and closed after the circuit of the second winding.

WIRT E. DARROW. GEORGE H. PETERSON. 

